So far, highly unsaturated fatty acids contained in fish oils have attracted a considerable attention as raw materials for medicaments or health foods, and a large number of products, such as eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), derived from fish oils have been placed on the market. As mentioned above, those highly unsaturated fatty acids have primarily been derived from fish oils as major raw materials, but raw fishes, which are natural sources for fatty acids, have an aspect that their availability and cost are unstable. In this situation, highly unsaturated fatty acids have been produced using microorganisms in place of fish oils in recent years. For example, a method for producing DHA by Crypthecodinium cohnii (Non-patent document 1) or a method for producing a fat-and-oil containing much arachidonic acid by a mould of Mortierellaceae (Patent documents 1 and 2) are known. These methods have been brought into practice.
In recent years, it has been known that highly unsaturated fatty acids are accumulated in Labyrinthula of stramenopiles (a group of mononuclear cellular eucaryotes which have hollow mastigonemes in flagella) (Non-patent document 2). In this situation, the production of DHA in Labyrinthula has been investigated in various ways, and microorganisms belonging to Schizochytrium (Non-patent document 3) or Ulkenia (Non-patent document 4) have practically been used. There is a limitation, however, in the ability of lipid accumulation and the content of DHA in the total fatty acids, and further there is a problem that the cost of DHA produced by microorganisms is higher than that derived from fish oils.
Patent document 1: JP-A-63-44891
Patent document 1: JP-A-63-12290
Non-patent document 1: Zvi Cohen et al., Single Cell Oils, (USA), AOCS Press, 2005, p. 86-98
Non-patent document 2: Nakahara et al., Journal of the American Oil Chemists' Society, 1996, Vol. 73, p. 1421-1426
Non-patent document 3: Zvi Cohen et al., Single Cell Oils, (USA), AOCS Press, 2005, p. 36-52
Non-patent document 4: Zvi Cohen et al., Single Cell Oils, (USA), AOCS Press, 2005, p. 99-106